Synovial fibroblasts.

Chronic synovitis refers to fibrin deposits on the surface of proliferating superficial synovial lining cells leading to villous hyperthrophy, and associated with foci of cell necrosis and infiltration of chronic inflammatory cells. The superficial synovial lining cells include fibroblast-like type B cells and macrophage-like type A cells. Fibroblast- and macrophage-like cells in the early or leading edge of pannus may represent an extension of these cells, which themselves may be nothing else than stromal fibroblasts and macrophages adapted to the particular micro-milieu prevailing at the interface of hyaluronate (HA) containing synovial fluid and richly vascularized loose connective tissue in the sublining stroma. In all three locations fibroblasts are exposed to various humoral substances, extracellular matrix (ECM) and cell-cell contacts, which may modify their phenotype and function. Therefore, one would expect differences in the fibroblasts in inflammatory and non-inflammatory synovial tissue. These changes can be best understood by considering some of the basic fibroblast properties, namely migration, substrate adherence, proliferation and synthesis and degradation of ECM.